Optical coherence tomography device for otitis media

ABSTRACT

An OCT apparatus and method for characterization of a fluid adjacent to a tympanic membrane has a low coherence source which is coupled to a splitter which has a measurement path and a reference path. The reference path is temporally modulated for length, and the combined signals from the reference path and the measurement path are applied to a detector. The detector examines the width of the response and the time variation when an optional excitation source is applied to the tympanic membrane, the width of the response and the time variation forming a metric indicating the viscosity of a fluid adjacent to the tympanic membrane being measured.

CROSS-REFERENCE

This application is a continuation of Ser. No. 15/188,750, filed Jun.21, 2016, which is incorporated herein by reference in its entirety andto which application we claim priority under 35 USC § 120.

FIELD OF THE INVENTION

The present invention relates optical coherence tomography (OCT). Inparticular, the device relates to OCT for use in the diagnosis of otitismedia (OM).

BACKGROUND OF THE INVENTION

Otitis Media is a common disease of the inner ear, involving tissueinflammation and fluidic pressure which impinges on the tympanicmembrane. Otitis Media may be caused by a viral infection, whichgenerally resolves without treatment, or a bacterial infection, whichmay progress and cause hearing loss or other deleterious andirreversible effects. Unfortunately, it is difficult to distinguishbetween viral or bacterial infection using currently availablediagnostic devices, and the treatment methods for the two underlyinginfections are quite different. For bacterial infections, antibioticsare the treatment of choice, whereas for viral infections, the infectiontends to self-resolve, and antibiotics are not only ineffective, but mayresult in an antibiotic resistance which would make them less effectivein treating a subsequent bacterial infection.

The definitive diagnostic tool for inner ear infections is myringotomy,an invasive procedure which involves incisions into the tympanicmembrane, withdrawal of fluid, and examining the effusion fluid under amicroscope to identify the infectious agent in the effusion. Because ofcomplications from this procedure, it is only used in severe cases. Thispresents a dilemma for medical practitioners, as the prescription ofantibiotics for a viral infection is believed to be responsible for theevolution of antibiotic resistance in bacteria, which may result in moreserious consequences later in life, and with no efficacious result, astreatment of viral infectious agents with antibiotics is ineffective. Animproved diagnostic tool for the diagnosis of otitis media is desired.

OBJECTS OF THE INVENTION

A first object of the invention is a non-invasive medical device for theidentification of fluid type adjacent to a tympanic membrane.

A second object of the invention is a method for identification of afluid adjacent to a tympanic membrane.

A third object of the invention is a method for performing opticalcoherence tomography for identification of a film characteristicadjacent to a tympanic membrane.

A fourth object of the invention is an apparatus for performing opticalcoherence tomography for identification of a fluid characteristicadjacent to a tympanic membrane.

A fifth object of the invention is an apparatus and method forcharacterization of a tympanic membrane and adjacent materials bycoupling a pressure excitation source to a tympanic membrane, where thetympanic membrane is illuminated through a measurement path by anoptical source having low coherence, the low coherent optical sourcealso coupled to a reference path and to a mirror, where reflections fromthe mirror and reflections from the tympanic membrane are summed andpresented to a detector, the reference path length modulated over arange which includes the tympanic membrane, the detector therebyreceiving reflected optical energy from the tympanic membrane throughthe measurement path and also from the mirror through the referencepath, such that modulation of the reference path length at asufficiently high rate allows for estimation of the tympanic membraneposition in response to the pressure excitation, thereby providingcharacterization of the tympanic membrane and adjacent fluid.

A sixth object of the invention is an optical coherence tomographysystem having a measurement path and a reference path, the referencepath modulated in length, the measurement path and reference pathcoupled through an optical splitter to an optical source having lowcoherence, where reflected optical energy from the reference opticalpath and reflected optical energy from the measurement optical path aresummed and provided to a wavelength splitter and thereafter to aplurality of detectors, one detector for each sub-range of wavelengthswithin the wavelength spectrum of the low coherence optical source, theplurality of detectors coupled to a controller discriminating bywavelength characteristics the detector response for at least twodifferent reflective materials.

SUMMARY OF THE INVENTION

An optical coherence tomography (OCT) device has a low coherence opticalsource generating optical energy coupled through a first splitter,thereafter to a second splitter, the second splitter having ameasurement optical path to a tympanic membrane and also a referenceoptical path to a reflector which returns the optical energy to thefirst splitter, where the reflected optical energy is added to theoptical energy reflected from the measurement optical path. The combinedreflected optical energy is then provided to the first splitter, whichdirects the optical energy to a detector. The reflector is spatiallymodulated in displacement along the axis of the reference optical pathsuch that the detector is presented with an optical intensity andoptionally a continuum of optical spectral density from a particularmeasurement path depth, when the measurement optical path and referenceoptical path are equal in path length. When the device is positionedwith the measurement path directed into an ear canal and directingoptical energy to a tympanic membrane, by varying the reference opticalpath length through translation of the location of the reflector alongthe axis of the reference optical path, a measurement of optical andspectral characteristics of the tympanic membrane may be performed.Additionally, an external pressure excitation may be applied to providean impulsive or steady state periodic excitation of the tympanicmembrane during the OCT measurement, and a peak response and associatedtime of the peak response identified. The temporal characteristics andpositional displacement of the tympanic membrane can be thereafterexamined to determine the tympanic membrane response to the externalpressure excitation. The evaluation of the tympanic membrane responsefrom the OCT detector data may subsequently be correlated to aparticular viscosity or biofilm characteristic. By examination of thetemporal characteristic, an estimate of the viscosity of a fluidadjacent to a tympanic membrane may be determined, and the viscositysubsequently correlated to the likelihood of a treatable bacterialinfection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an optical coherence tomographycharacterization system.

FIG. 2A shows a plot of mechanical actuator displacement vs actuatorvoltage.

FIG. 2B shows a plot of reference path length over time, as controlledby actuator voltage or current.

FIG. 3 shows a block diagram for an optical coherence tomographycharacterization system for use examining a tympanic membrane.

FIG. 4 shows a polychromatic detector.

FIG. 5A shows a plot of an example excitation waveform for modulation ofa reference length

FIG. 5B shows a detector signal for a tympanic membrane adjacent tofluid such as from OME and a detector signal for a normal tympanicmembrane.

FIG. 6 shows an optical waveguide system for measurement of a tympanicmembrane.

FIG. 7 shows an optical waveguide system for measurement of a tympanicmembrane with an excitation source.

FIG. 8A shows a plot for a sinusoidal excitation applied to deformablesurface or membrane with a reflected response signal.

FIG. 8B shows a plot for a step excitation applied to a deformablesurface or membrane, and a response to the step excitation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram for an optical coherence tomography (OCT)device according to one example of the invention. Each reference numberwhich appears in one drawing figure is understood to have the samefunction when presented in a different drawing figure. A low coherencesource 102 such as a broadband light emitting diode (LED) with acollimated output generates optical energy along path 104 to firstoptical splitter 106, and optical energy continues to second opticalsplitter 108, where the optical energy divides into a measurementoptical path 118 and a reference optical path 112, which include thesegment from second splitter 108 to mirror 110 to path length modulator114. The optical energy in the measurement optical path 118 interactswith the tympanic membrane 120, and reflected optical energycounter-propagates to the detector via path 118, where it is joined byoptical energy from reference optical path 112 reflected from mirror 110and splitter 108, and the combined reflected optical energy propagatesto first splitter 106, thereafter to mirror 105, and to detector 124 viapath 122. Detector 124 generates an electrical signal corresponding tothe intensity of detected optical energy on path 122, which is a steadystate maximum when the path length for reflected optical energy from thetympanic membrane is exactly the same length as the reference opticalpath, and a temporal maximum if the reference optical path length isswept over a range, such as by actuating path length modulator 114 overtime. Each type of reflective membrane will produce a characteristicdetector signal. For example, as the reference path length traversesthrough a thin membrane boundary such as a healthy tympanic membrane, asingle peak will result corresponding to the single reflective region ofthe tympanic membrane. If the reference path length is through a fluidicear such as one containing low-viscosity infectious effusion, an initialpeak of the tympanic membrane reflection will subsequently generate aregion of extended reflection with an amplitude that drops from opticalattenuation of the reflected signal. If the reference path lengthtraverses through the tympanic membrane with a bacterial infection, abacterial film may be present on the opposite surface of the tympanicmembrane, which may produce a greater axial extent of reflection,followed by a pedestal indicating a high scattering coefficient andcorresponding increased attenuation. Additionally, the three types offluid viscosities behind the tympanic membrane (air vs thin fluid vsthick fluid) will respond differently to pressure excitations generatedon the tympanic membrane. Accordingly, is possible to modulate thereference optical path length and optionally the pressure adjacent tothe tympanic membrane, and examine the nature of the detector outputsignal and response to excitation pressure to determine the presence orabsence of fluid adjacent to the tympanic membrane, the presence orabsence of a biofilm such as bacteria adjacent to the tympanic membrane,and the viscosity of fluid adjacent to the tympanic membrane, all frommovement of the tympanic membrane on the measurement optical path aspresented at the detector output.

In one example of the present invention, the path length modulator 114varies the reference path length by a distance corresponding to themeasurement path length from 126 a to 126 d of FIG. 1 , corresponding toa region of movement of a tympanic membrane 115 to be characterized. Asmodulator 114 increases the reference path length, the signal deliveredto the detector is closer to region 126 d and when modulator 114decreases the distance of the reference path length, the region signaldelivered to the detector is in region 126 a.

FIG. 2A shows an example relationship between actuator voltage orcurrent and axial displacement of path length modulator 114, which isdriven by a mechanical driver circuit 116, which may be a voice coildriver for a voice coil actuator coupled to mirror 114, modulating themirror about the optical axis of 112. The type of driver and path lengthmodulator 114 is dependent on the highest frequency of displacementmodulation, since the energy to displace path length modulator 114 isrelated to the mass of the path length modulator 114, such as the caseof a moving mirror. The mirror and actuator may be micro electricalmachined system (MEMS) for lower reflector mass and correspondinglyfaster mirror response. It may be possible to utilize a variety of otherpath length modulators without limitation to the use of mirrors.

FIG. 2B shows the controller 117 generating an actuator voltage in astep-wise manner, with the actuator stopping momentarily at each depth.For example, if increased actuator drive results in a longer referencepath length, then from T1 to T2, the actuator voltage may be 202 a,corresponding to the displacement position 126 a of FIG. 1 , and theother voltages 202 b, 202 c, and 202 d may correspond to positionsadjacent to the tympanic membrane of 126 b, 126 c, and 126 d,respectively.

FIG. 3 shows an example OCT tympanic membrane characterization system302 with the elements arranged to provide a single measurement output.For the case of free-space optics (optical energy which is not confinedwithin a waveguide such as an optical fiber), the system splitters andcombiners of FIGS. 1 and 3 are partially reflective mirrors. Theprincipal elements show in FIG. 3 correspond to the same functionalelements of FIG. 1 . By rearrangement of the reference optical path, theelements of the system may be enclosed, as shown.

In one example of the invention, detector 124 may be a singleomni-wavelength optical detector responsive to the total applied opticalintensity, and having a characteristic response. In another example ofthe invention detector 124 may include a single wavelength filter, or achromatic splitter and a plurality of detector elements, such that eachreflected optical wavelength may be separately detected. FIG. 4 showscollimated optical energy 122 entering chromatic detector 124A, where itis split into different wavelengths by refractive prism 124B, whichseparates the wavelengths λ1, λ2, λ3, λ4 onto a linear or 2D detector124C, which is then able to provide an intensity map for the reflectedoptical energy by wavelength. Individual detection of wavelengths may beuseful where the signature of wavelength absorption is specific to aparticular type of bacteria or tympanic membrane pathology. The spectrumof detector response is typically tailored to the reflected opticalenergy response, which may be in the IR range for an OCT system withmore than a few mm of depth measurement capability. In one example ofthe invention, the detector spectral response for various biologicalmaterials is maintained in a memory and compared to the superposition ofresponses from the plurality of optical detectors. For example, theoptical reflective characteristics of cerumen (earwax), a healthytympanic membrane, an inflamed tympanic membrane (a tympanic membranewhich is infused with blood), a bacterial fluid, an effusion fluid, andan adhesive fluid may be maintained in a template memory and compared tothe spectral distribution of a measured tympanic membrane response overthe axial depth of data acquisition. The detector response at each axialdepth over the range of reference optical path length can then becompared to the spectral characteristics of each of the template memoryspectral patterns by a controller, with the controller examining thedetector responses for each wavelength and the contents of the templatememory and estimating the type of material providing the measurementpath reflection based on this determination. The detection of a spectralpattern for cerumen may result in the subtraction of a cerumen spectralresponse from the detector response, and/or it may result in anindication to the user that earwax has been detected in the response,which the user may eliminate by pointing the measurement optical path ina different region of the tympanic membrane.

Because the axial resolution of the optical coherence tomography isfractions of an optical wavelength, it is possible to characterize eachof the structures separately on the basis of optical spectrum, eventhough each of the structures being imaged is only on the order of ahundred microns in axial thickness. The axial resolution of the systemmay be improved by providing a very narrow optical beam with highspatial energy along the measurement axis and over the axial extent ofthe tympanic membrane.

FIGS. 5A and 5B show an example of the invention for use in detectingposition of a tympanic membrane over time. The controller 117 generatesa triangle waveform 502 for use by the path length modulator, whichdirects the optical energy to the tympanic membrane, which may havefluid adjacent to it, and the fluid may have a particular viscosity,which may be known to increase during the progression of a bacterialinfection. Bacterial infections are known to provide a biological filmon the surface of a membrane, such as the tympanic membrane, withspecific optical reflection characteristics. The optical signal isdirected through the outer ear canal towards the tympanic membrane to becharacterized, and the detector responses of FIG. 5B are examined bycontroller 117 of FIG. 3 . A first set of waveforms 509 shows a timedomain response which includes an initial peak 507 associated with thestrong reflection of the sharp reflective optical interface provided bythe tympanic membrane at a first reflective interface, and the fluidbehind the tympanic membrane also generates a signal which attenuateswith depth, shown as a sloped pedestal 508. The presence of pedestal 508indicates the presence of fluid behind the tympanic membrane. This maybe contrasted with the second set of responses 511 for a normal tympanicmembrane, such as the peak of waveform 522, which is comparativelynarrow and of shortened duration 520, as reflective fluid is not presentbehind the tympanic membrane.

In an additional embodiment of the invention, the tympanic membraneitself may be modulated by an external excitation source, such as an airpuff, or a source of air pressure which is modulated over time. Where anexternal pressure excitation source is provided, and the pressureexcitation is selected to provide less than 1% displacement of thetympanic membrane, for example, the relative temporal position of thepeak optical signal will indicate the position of the tympanic membrane.Because the refresh rate of the system is optical, rather than acousticof prior art ultrasound devices, the speed of interrogation of thetympanic membrane is only limited by the rate of modulation of the pathlength modulator 114, which may be several orders of magnitude fasterthan an ultrasound system. Additionally, the axial resolution of anoptical system relying on optical interferometry is much greater thanthe axial resolution of an ultrasound system which is governed bytransducer ringdown. Additionally, because the acoustic impedanceboundary between air and the tympanic membrane is extremely large, theultrasound penetration depth of ultrasound to structures beyond thetympanic membrane is very limited. By contrast, the optical index ofrefraction ratio from air to tympanic membrane is many orders ofmagnitude lower than the ultrasound index of refraction ratio acrossthis boundary, so the optical energy loss at the interface is lower. Theoptical penetration is primarily bounded by the scattering lossesassociated with the tympanic membrane and structures beyond the tympanicmembrane interface, and these losses may be mediated in part by using avery high optical energy which is pulsed with a duty cycle modulation tomaintain the average power applied to the tympanic membrane in areasonable average power range.

FIG. 6 shows a fiber-optic example of an optical coherence tomographysystem 600. Controller 618 coordinates the various subsystems, includingenabling low coherence source 602, which couples optical energy to anoptical fiber 604, which delivers this optical energy thereafter to afirst splitter 606, thereafter to optical fiber 608 and to secondsplitter 610. Optical energy from second splitter 610 is directed downtwo paths, one a measurement path 612 with length Lmeas 615 to atympanic membrane, and the other to reference optical path 617 withlength Lref and terminating into an open reflective fiber end 619, whichmay alternatively be a mirrored polished end or optical reflectivetermination, with the optical path 617 including an optical fiberwrapped around a PZT modulator 614, which changes dimensional shape anddiameter when an excitation voltage is applied to the PZT. When the PZTmodulator 614 is fed with a sine wave or square wave excitation, the PZTmodulator 614 increases and decreases in diameter, thereby providing avariable length Lref. The PZT modulator 614 is also capable of highspeed fiber length modulation in excess of 100 Khz in frequency. Otherfiber length modulators known in the art may be used for rapidlychanging the length of optical fiber on the Lref path, with the PZTmodulator 614 shown for reference only. The combined optical energy fromthe Lmeas path and Lref path reach the second splitter 610 and return onfiber 608, comprising the sum of optical energy reflected from PZTmodulator 614 and reflected from the tympanic membrane 650. The combinedoptical energy travels down path 608 to first splitter 606, throughfiber 620, and to detector 622, where the coherent optical energysuperimposes and subtracts, forming a detector 622 output accordingly,which is fed to the controller 618 for analysis. The controller 618 alsogenerates the PZT modulator excitation voltage 616, such as the voltageor current waveform 502 of FIG. 5A, and may also generate a signal toenable the low coherence source 602, and perform analysis of thedetector 622 response, which may be a single intensity value over thewavelength response of the detector 622, or the individual wavelengthoutput provided by the sensor of FIG. 4 . The controller acts on thedetector responses in combination with the Lref modulation function todetermine an effusion metric which may be correlated to the likelihoodof fluid being present adjacent to a tympanic membrane, and also providean indication of the viscosity of the fluid adjacent to the tympanicmembrane.

FIG. 7 shows an extension of FIG. 6 with an external tympanic membraneexcitation generator 704 which delivers miniscule pressure changes suchis actuated by a voice coil actuator or other pressure source,preferably with peak pressures below 50 deka-pascals (daPa) forapplication to a tympanic membrane. The modulation of the reference pathlength by the PZT modulator 614 is at a rate which exceeds the highestfrequency content of the excitation generator 704 by at least a factorof 2 to satisfy the Nyquist sampling requirement.

In one example of the invention, the reference path length is modulatedby a first modulator and second modulator operative sequentially, wherethe first modulator provides a large but comparatively slow referencepath length change, and the second modulator provides a small butcomparatively fast reference path length change. In this manner, thefirst modulator is capable of placing the region of OCT examinationwithin a region of interest such as centered about a tympanic membrane,and the second modulator is capable of quickly varying the path lengthto provide a high rate of change of path length (and accordingly, a highsampling rate) for estimation of tympanic membrane movement in responseto the pressure excitation.

It can be seen in the tympanic membrane shown as 115 in FIGS. 1 and 3,and 650 in FIGS. 6 and 7 , that the tympanic membrane has a conicalshape with a distant vertex (119 of FIGS. 1 and 3, 651 of FIGS. 6 and 7), which is known in otolaryngology as the “cone of light”, as it is theonly region of the tympanic membrane during a clinical examination whichprovides a normal surface to the incident optical energy. Similarly,when using an ultrasonic source of prior art systems, the cone of lightregion is the only part of the tympanic membrane which providessignificant reflected signal energy. The optical system of the presentinvention is operative on the reflected optical energy from the surface,which need not be normal to the incident beam for scattered opticalenergy, thereby providing another advantage over an ultrasound system.

FIG. 8A shows an example sinusoidal pressure excitation from excitationgenerator 704 applied to a tympanic membrane, such as a sinusoidalwaveform 821 applied using a voice coil diaphragm actuator displacing avolume sufficient to modulate a localized region of the tympanicmembrane or surface pressure by 100 daPa (dekapascals) p-p. Sub-sonic(below 20 Hz) frequencies may require sealing the localized regionaround the excitation surface, whereas audio frequencies (in the range20 Hz to 20 kHz) and super-audio frequencies (above 20 kHz) may besufficiently propagated as audio waves from generator 704 withoutsealing the ear canal leading to the tympanic membrane to becharacterized. The sinusoidal pressure excitation 821 results in amodulation of the surface, which is shown as plot 832, as the modulationin surface position corresponds to a change in the associated Lref pathlength by the same amount. Each discrete circle of waveform 832represents a sample point from the OCT measurement system 700,corresponding to the Lref path length and change in tympanic membraneposition, with each point 332 representing one such sample. In oneexample embodiment of the invention, a series of sinusoidal modulationexcitation 821 frequencies are applied, each with a different period822, and the delay in response 830 and peak change in Lref are used incombination to estimate the ductility or elasticity of the tympanicmembrane, fluid viscosity, or other tympanic membrane or fluid property.In the present examples, there is a 1:1 relationship between thedisplacement of the tympanic membrane and associated change in pathlength of the reference path which results in the peak response. Forexample, if the scale of FIG. 5B is a sequence of 0, −0.5 mm, −1 mm,−0.5 mm, 0 mm, 0.5 mm, etc, then this represents a correspondingdisplacement in the tympanic membrane by these same distances. Byapplying a series of audio and sub-audio tones with various cycle times822 and measuring the change in Lref as shown in plot 832, it ispossible to estimate the displacement of the tympanic membrane andextract frequency dependent characteristics such as viscosity orelasticity of the fluid behind the tympanic membrane. For example, anexemplar elasticity metric measurement associated with the changeddensity or viscosity of the fluid could be an associated change insurface or membrane response time 874 for a step change, or phase delay830 for a sinusoidal frequency. In this manner, a frequency domainresponse of the surface may be made using a series of excitations 821and measuring a series of surface responses 832. The reference pathmodulator 614 of FIGS. 6 and 7 , or mirror 114 of FIG. 3 , may include afirst path length modulator which centers the reference path length toinclude the tympanic membrane, and a second path length modulator whichrapidly varies the reference path length to provide adequate sampling ofthe axial movement of the tympanic membrane.

Whereas FIG. 8A shows a sinusoidal excitation which may be provided in aseries of such excitations to generate a phase vs. frequency responseplot of the surface displacement from the series of measurements, FIG.8B shows a time domain step response equivalent of FIG. 8A, where asurface step pressure excitation 862 of 50 daPa peak is applied to thetympanic membrane, which generates the measured tympanic membranedisplacement sequence 872. It is similarly possible to characterize thesurface response based on a time delay 874 and amplitude response (shownas 0.5 mm) for displacement response plot 872.

In one example of the invention, a separate low-coherence optical source102 or 602 such as an infrared range source is used for increasedpenetration depth, and a separate visible source (not shown) is usedco-axially to indicate the region of the tympanic membrane beingcharacterized while pointing the measurement optical path onto thetympanic membrane. The optical source 102 or 602 may be an infraredsources to reduce scattering, thereby providing additional depth ofpenetration. In another example of the invention, the low-coherenceoptical source 102 or 602 is a visible optical source, thereby providingboth illumination of the tympanic membrane region of interest, and alsomeasurement of displacement of the tympanic membrane, as previouslydescribed.

The present examples are provided for understanding the invention, it isunderstood that the invention may be practiced in a variety of differentways and using different types of waveguides for propagating opticalenergy, as well as different optical sources, optical detectors, andmethods of modulating the reference path length Lref. The scope of theinvention is described by the claims which follow.

What is claimed is:
 1. A method for diagnosing otitis media of a patientwith a tympanic membrane (TM) characterization system, the methodcomprising: (a) providing a non-contact force through an air medium toone or more of the tympanic membrane or a fluid adjacent thereto,wherein the non-contact force is provided without sealing an ear canalof the patient leading to the tympanic membrane or the fluid adjacentthereto; (b) directing a first optical energy along a measurement pathwith the TM characterization system, wherein the measurement pathcrosses a tympanic membrane and a fluid adjacent the tympanic membrane,wherein the first optical energy interacts with one or more of thetympanic membrane or the fluid adjacent the tympanic membrane; (c)directing a second optical energy along a reference path with the TMcharacterization system; (d) combining the first optical energy and thesecond optical energy at a detector, with the TM characterizationsystem, after the first optical energy has interacted with the one ormore of the tympanic membrane or the fluid adjacent the tympanicmembrane and the first and second optical energies have traversed themeasurement and reference paths, respectively, the combined first andsecond optical energies generating a first detector response at thedetector; (e) changing a length of the reference path and receiving asecond detector response of the combined first and second opticalenergies based on a change in reference path length induced by thenon-contact force with the TM characterization system; (f) determining amembrane metric from the first and second detector responses, whereinthe membrane metric comprises an elasticity of the tympanic membrane,viscosity of the fluid adjacent the tympanic membrane, or anycombination thereof; and (g) determining whether the patient has abacterial ear infection and whether the patient has an ear infectionwith a low-viscosity infectious effusion with the TM characterizationsystem based on the membrane metric.
 2. The method of claim 1, whereinthe membrane metric comprises an effusion metric correlated to alikelihood of fluid being present adjacent to the tympanic membrane. 3.The method of claim 1, wherein determining the membrane metric furthercomprises determining at least one of (i) a width of the detectorresponses, (ii) a pedestal width of the detector responses, or (iii) areflected wavelength profile of the detector responses.
 4. The method ofclaim 3, wherein determining the membrane metric further comprises (i)examining the pedestal width of the detector responses and an arrivaltime of peak responses at the detector, (ii) comparing the peakresponses to reference peak responses, and (iii) comparing the pedestalwidth and the arrival time of the peak responses.
 5. The method of claim1, wherein the first and second detector responses comprise wavelengthdependent responses.
 6. The method of claim 5, further comprisingcomparing the wavelength dependent responses to template responses of atleast one known material.
 7. The method of claim 6, wherein the templateresponses comprise template responses of at least one of cerumen,healthy tympanic membrane, inflamed tympanic membrane, bacterial fluid,effusive fluid, or adhesive fluid.
 8. The method of claim 1, furthercomprising indicating a presence of at least one of cerumen, healthytympanic membrane, inflamed tympanic membrane, bacterial fluid, effusivefluid, or adhesive fluid to a user.
 9. The method of claim 1, whereinthe non-contact force comprises a pressure excitation.
 10. The method ofclaim 1, wherein the non-contact force comprises an impulsiveexcitation.
 11. The method of claim 1, wherein the non-contact forcecomprises a periodic excitation.
 12. The method of claim 11, wherein afrequency of the periodic excitation is within a range from 20 Hz to 20kHz.
 13. The method of claim 1, further comprising determining one ormore of a position or displacement of the tympanic membrane based on themembrane metric.
 14. The method of claim 1, wherein (f) comprisesdetermining the membrane metric from the first and second detectorresponses and the changing of the length of the reference path, whereinthe first and second detector responses are in response to thenon-contact force, and wherein the membrane metric is determined fromthe first and second detector responses in response to the non-contactforce.
 15. The method of claim 1, wherein changing the length of thereference path comprises temporally modulating the length of thereference path.
 16. The method of claim 1, wherein the non-contact forceincludes displacing the tympanic membrane, and wherein the first andsecond detector responses is generated as a function of (i) a length ofthe reference path and (ii) a displacement of the tympanic membrane overtime.
 17. The method of claim 1, further comprising determining thepresence or absence of a thick fluid behind the tympanic membrane. 18.The method of claim 17, wherein step (g) comprises determining apresence or absence of a thin fluid behind the tympanic membrane. 19.The method of claim 1, wherein the membrane metric comprises optical andspectral characteristics.